The present invention relates to the manufacturer of solenoid coils for electrically actuated control devices such as water inlet valves employed for use on household washing machines and dishwashers. Valves of this type generally are activated by an electrical programmer timer which is capable of handling only a very limited current flow to the electrical valve actuator. The limited power handling capability of the programmer timer requires that the valve actuator provide the required mechancial actuating force from a minimum of current flow to the solenoid. This necessarily has resulted in solenoid coils which have been wound from many hundreds of turns of extremely fine single conductor wire.
In the manufacture of fine wire electrical valve actuating solenoids in high volume or mass production, it has proven difficult to provide a connection between the ends of the coil conductor and the electrical attachment terminals provided for attachment to the appliance wiring harness. It has been found particularly troublesome to provide a way or means of attaching the coil wire ends to the terminals in the very short time, on the order of a few seconds, allotted for operations in a high speed coil manufacturing process.
The fine wire conductor has been found to be difficult to manipulate automatically by non-human means since the breaking strength of the fine wire is quite low. The fine wire does not lend itself to devices and operations which exert any substantial tension on the wire. This has proven particularly troublesome where the fine coil wire is wound at a rapid rate about a connector terminal for termination thereon. The fine wire conductor is not capable of withstanding sufficient tension to permit lead termination safely by tying or other friction-dependent techniques for providing metal-to-metal contact of the wire with a connector terminal. It has thus been found desireable to provide a soldered connection for the wire termination onto the connector terminal in order to provide the least amount of electrical resistance to current flow between the terminal and the coil wire.
The accomplishment of the soldering of a fine coil wire to a connector terminal in the very short time allotted on a high speed production basis, has generated a need for a technique of soldering the wire-terminal connection very rapidly on an easily controlled and repeatable basis.
In providing a high-speed, or short-cycle duration, soldering process for fine wire coil leads to a connecting terminal a very rapid heating of the terminal and wire has been required to provide a rapid flowing of the solder onto the joint for effecting adequate electrical connection there-between. The rapid heating of the terminal has resulted in the terminal and wire lead reaching a temperature substantially in excess of the melting point of the solder. In fact, it has been found that the terminal will be heated to nearly the red zone and consequently subjected to rapid and undesired oxidation of the terminal surface. This undesired oxidation has prevented the solder from adequate adhesion to the surface of the terminal and has resulted in a poor solder connection.
It has thus been desired to find a way or means of rapidly soldering the ends of a fine wire solenoid coil to connector terminals in a manner providing a good solder joint and yet maintaining the soldering operations cycle of such a short time duration as to enable high-speed production of the completed coil assembly.